Worn out tyres are associated with special problems, both regarding recycling and disposal on waste disposal/landfill sites. In addition to containing a rubber matrix comprising natural and/or synthetic rubber, modern tires also contain carbon black, plastisizers, cross-linkers, anti-oxidants, anti-ozone agents and other performance-improving additives plus metal or fibre reinforcement.
In addition to taking up a great deal of space on waste disposal sites, the dumping of tires causes several other problems as well. The shape of the tires causes it to slowly but surely migrate up to the surface of the disposal site and thereby greatly disrupt the degradation process. Tires also have a long life as they are manufactured to resist both thermal and biological degradation as well as mechanical wear. Furthermore, tires resist ultraviolet radiation, ozone and other oxidants, as well as water and ice. Fires in a used tires depot are especially problematic as they have proven to be very difficult to extinguish. In addition, the fire releases toxic substances both in the smoke and in the water used to extinguish the blaze.
Problems also occur when tires are used as a source of combustion, among other reasons, because of their content of sulphur but also because they contain metals and chemicals.
As no one has so far succeeded in developing a large scale method for devulcanising recycled rubber, this is difficult to use to any great extent in the production of new tires. At present, no more than 2% of old rubber is used in new tires. The problem can be partially overcome by modifying the surface of the rubber particles. Surface modification of rubber particles from ground down tires is a technique that means that the very outer layer of the rubber particles is modified to allow improved adhesion when combined with other materials, e.g. other elastomers. The technique involves exposing the rubber particles to a powerful reactive gas, e.g. fluorine. It is, therefore, not without its problems.
The reuse of rubber from tires has so far been focused on relatively uncomplicated applications, such as blasting mats, mixing in asphalt or in the production of low vibration flooring. Sheared fragments of rubber or rubber granulate can even be used as such, for purposes as improving soil, filling material for building work, e.g. road construction for recreation or trotting tracks, etc. Mixing in with compost has also been suggested. The problem of leaching of metals and poly-aromatic hydrocarbons that can be taken up by the biosystem is nevertheless associated with these applications.
Bearing in mind this background, there is thus a need for new, functional and beneficial materials with a high content of recycled vulcanised rubber.